Braze alloy layered product

ABSTRACT

The present invention relates to a method for providing a braze alloy layered product comprising the following steps: —applying at least one silicon source and at least one boron source on at least a part of a surface of a substrate, wherein the at least one boron source and the at least one silicon source are oxygen free except for inevitable amounts of contaminating oxygen, and wherein the substrate comprises a parent material having a solidus temperature above 1100° C.; —heating the substrate having the applied boron source and the applied silicon source to a temperature lower than the solidus temperature of the parent material of the substrate; and cooling the substrate having the applied boron source and the applied silicon source, and obtaining the braze alloy layered product. The present invention relates further to a braze alloy layered product, a method for providing a brazed product, a method for providing a coated product, and uses of the braze alloy layered product.

The present invention relates to a novel brazing concept, a method forproviding a braze alloy layered product, a braze alloy layered productobtained by the method, a braze alloy layered product. The presentinvention relates further to a method for providing a brazed product, tobrazed product obtained by the method, to a method for providing acoated product, and uses of a braze alloy layered product.

BACKGROUND

Today there are different joining methods for joining together alloyshaving high melting temperatures. By high temperature a meltingtemperature higher than 900° C. is intended. One common method which isused is welding. Welding refers to a method wherein the base materialwith or without additional material is melted, i.e. creation of a castproduct via melting and re-solidification. Another joining method isbrazing. During the brazing process a braze filler is added to the basematerial, and the braze filler is melted during the process at atemperature above 450° C., i.e. forming a liquid interface, at atemperature lower than liquidus temperature of the base material to bejoined. When brazing the liquid interface should have good wetting andflow. Soldering is a process in which two or more metal items are joinedtogether by melting and flowing of a filler metal, i.e. a solder, intothe joint, the solder having a lower melting point than the work-piece.In brazing, the filler metal melts at a higher temperature than thesolder, but the work-piece metal does not melt. The distinction betweensoldering and brazing is based on the melting temperature of the filleralloy. A temperature of 450° C. is usually used as a practicaldelineating point between soldering and brazing.

When brazing a braze filler is applied in contact with the gap or theclearance between the base material to be joined. During the heatingprocess the braze filler melts and fills the gap to be joined. In thebrazing process there are three major stages the first stage is calledthe physical stage. The physical stage includes wetting and flowing ofthe braze filler. The second stage normally occurs at a given joiningtemperature. During this stage there is solid-liquid interaction, whichis accompanied by substantial mass transfer. The base material volumethat immediately adjoins the liquid filler metal either dissolves or isreacted with the filler metal in this stage. At the same time a smallamount of elements from the liquid phases penetrates into the solid basematerial. This redistribution of components in the joint area results inchanges to the filler metal composition, and sometimes, the onset ofsolidification of the filler metal. The last stage, which overlaps thesecond, is characterized by the formation of the final jointmicrostructure and progresses during solidification and cooling of thejoint.

A method closely related to welding and brazing is diffusion brazing(DFB) also called Transient Liquid-phase bonding (TLP), or ActivatedDiffusion Bonding (ADB). Sometimes diffusion bonding is mentioned, butdiffusion bonding refers to diffusion brazing or diffusion welding andnow diffusion bonding is considered to be a non-standard term.

Diffusion brazing (DFB), Transient Liquid-phase bonding (TLP), orActivated Diffusion Bonding (ADB) is a process that coalesces, or joins,metals by heating them to a suitable brazing temperature at which eithera preplaced filler metal will melt or flow by capillary attraction or aliquid phase will form in situ between two surfaces in contact with eachother. In either case, the filler metal diffuses into the base materialuntil the physical and mechanical properties of the joint become almostidentical to those of the base metal. Two critical aspects of DFB, TLP,or ADB are that:

-   -   a liquid must be formed and become active in the joint area; and    -   extensive diffusion of the filler metal elements into the base        material must occur.

Ways of obtaining a joint close or the same as the one obtained whenDFB, TLP, or ADB is used, but has the advantage of brazing, e.g havingthe possibility to braze larger gaps etc, is by using a brazingtechnique and braze fillers disclosed by WO 2002/38327, WO 2008/060225and WO 2008/060226. By using a braze filler, i.e. a braze alloy, with acomposition close to the base material but with added melting pointdepressants, e.g. silicon and/or boron and/or phosphorus. By doing thisthe braze joint will have a composition close to the base material afterbrazing since braze filler had a similar composition as the basematerial, the braze filler blends with the base material due todissolution of the base material and the melting point depressantsdiffuses into the base material.

There are many reasons for selecting a certain joining method, such ascost, productivity, safety, speed and properties of the joined product.Closely related E-modules will decrease the risk of high stresses in thematerial with higher E-module when the material is loaded. When thethermal expansion coefficient is similar the result will decrease thethermally induced stresses. When the electrochemical potential issimilar the result will decrease the risk for corrosion.

The use of fillers, i.e. alloys, when joining base metals is acomplicated process. The filler has to be in a form that could beapplied to the base metal before heating. Usually the fillers areparticles suitably produced by atomization, but the fillers may also bein form of foils produced by “melt-spinning”, i.e. rapid solidification(RS). Regarding RS only a limited number of compositions are possible toproduce by RS. The number of compositions that can be made as particles,i.e. powder, is greater and the normal production of powders is byatomizing. When the fillers are in form of powders then they are oftencombined with binders to form a paste, which could be applied to thebase metal in any suitable way. To produce foils or to produce alloypowders are complicated processes and therefore costly. When powders areused the powders are suitable applied in form of a paste as mentionedabove, this will add an extra step to the process since the paste needto be blended with the binders and other components, which arebeneficial for the paste's properties. For both processes a great amountof work is carried out to get the right form, properties, shape andcomposition of the filler before melting and joining.

THE INVENTION

A purpose for the invention is to reduce the process steps when joiningsubstrates of parent materials. Another purpose is to simplify thejoining of the parent materials and thus reduce costs.

If possible, when selecting braze fillers, a composition close to theparent material is beneficial, since the parent material has beenselected for the product purposes. If it would have been possible andcost was no limit, it would be best to develop one braze filler for eachparent material. Therefore, another purpose with the invention is todecrease the needed number of braze fillers.

Accordingly, the present invention provides a solution to the technicalproblems and purposes by the novel and inventive brazing concept. Thefirst aspect relates to a method for providing a braze alloy layeredproduct comprising the following steps:

Step (i) applying one or more silicon sources and one or more boronsources on at least a part of a surface of a substrate, wherein the atleast one boron source and the at least one silicon source are oxygenfree except for inevitable amounts of contaminating oxygen, and whereinthe substrate comprises a parent material having a solidus temperatureabove 1100° C.;

Step (ii) heating the substrate having the applied boron source and theapplied silicon source to a temperature lower than the solidustemperature of the parent material of the substrate; and

Step (iii) cooling the substrate having the applied boron source and theapplied silicon source, and obtaining a braze alloy layered product.

Substrate is parts of an obtainable product, the parts could be forinstance but not limited to thick parts such as separators or decantersetc. or thin parts such as plates or coils, i.e. the substrate could beany parts that should be joined or coated. Substrate could also bework-pieces. The substrates may be of parent materials, i.e. material tobe brazed.

Parent material is a metal or an alloy. Alloy is defined as an intimateassociation or compound of two or more elements, the alloy possessing amarked degree of all or most of those characteristics commonly describedas metallic. Alloys are compounds not mere mixtures. Metal refers to anelement which has metallic properties.

Examples of parent materials according to the first aspect may be parentmaterials found in the list in Table 1, the parent materials are notlimited to the list and is just examples of possible parent materials.

TABLE 1 Approximate. solidus Approximate. liquidus temperaturetemperature Parent materials [° C.] [° C.] Nickel 200/201 1435 1445Nicrofer 5923hMo 1310 1360 Hastelloy ® C-2000 ® 1328 1358 AlloyHastelloy B3 1370 1418 Alloy C22 1357 1399 Inconel 625 1290 1350 Alloy C276 1325 1370 Nicrofer 3033 1330 1370 Nicrofer 3127HMo 1350 1370 AL6XN1320 1400 254SMO 1325 1400 Monel 400 1299 1348 Mild steel 1505 1535Stainless steel Type 316 1390 1440 Stainless steel type 304 1399 1421

Depending on which parent material is used, there are differentpreferred parent materials having different solidus temperature, i.e.the temperature point at which a material solidifies. According to oneexample the solidus temperature of the parent material may be above1100° C. According to another example the solidus temperature of theparent material may be above 1220° C. According to another example thesolidus temperature of the parent material may be above 1250° C.According to a further example the solidus temperature of the parentmaterial may be above 1300° C.

Compounds are combinations of two or more elements. Glass, steel, ironoxide are substances wherein every atom is attracted by all the adjacentatoms so as to make a uniform or very nearly uniform solid, such bodiesare clearly not mere mechanical mixtures, chemical compounds of varyingor indefinite composition such as silicates, polymers are chemicallycombined but are compound of varying compositions.

Without being bound to any specific theory, the inventors believe thatthe presence of boron provides for wettability and for lowering of themelting point, and the silicon provides for lowering of the meltingpoint.

A boron source refers to elemental boron (B), an alloy or compoundcontaining boron.

A silicon source refers to elemental silicon (Si), an alloy or compoundcontaining silicon.

According to a further example the method comprises a blend of the atleast one boron source and the at least one silicon source, and theblend is a mechanical blend.

A mechanical blend of powders refers to mechanical mixing of two or morecomponents. The mechanical blend of powders are particles from differentsources, each particles is either a boron source or a silicon source.

Contaminating oxygen refers to inevitable amounts of oxygen which forinstance is contained in technical grades etc. of a silicon source or ofa boron source, and the amount may be as high as 5 wt % oxygen in theboron source and as high as 5 wt % in the silicon source. Thecontaminating oxygen may be as high as 10 wt %.

The amount of silicon and boron in the blend depends on purity ofsilicon and boron, but also on the type of silicon source or boronsource which are contained in the blend. For instance if the siliconsource is Fe—Si the Fe is heavy and the amount of silicon and boron willbe lower. In Table 2 there are a few examples.

TABLE 2 B₄C, Amount Fe—B, Weight of Fe—Si, Total of B + Si Blend B or SiNi—B Si B weight B + Si [wt %] Si/B₄C 10.0 2.6 2.0 12.6 12.0 95.2Si/Fe—B 10.1 12.5 2.0 22.6 12.1 53.5 B/Fe—Si 2.0 30.2 10.1 32.6 12.137.6 Si/Ni—B 10.1 13.0 2.0 23.1 12.1 52.4

According to one example the method may comprise applying on the metalsubstrate a blend of one or more silicon sources and one or more boronsources, and a weight ratio in the blend of boron and silicon is withina range from about 3:100 wt:wt to about 100:3 wt:wt, and wherein siliconand boron are present in the blend in at least 25 wt %.

A blend of the present invention is advantageous in that it providespossibilities to obtain joints between substrates. The obtained jointsare of similar material as the material(s) of the substrates except thatthe joints contain additional amounts of the elements of the blend. Byallowing the formation of joints of the material in the substratesaccording to the novel brazing concept, the corrosion risks can beavoided or at least lowered since there will be less differences betweenthe material in the joints and the substrate compared to when commercialbrazing materials are used.

One advantage of a weight ratio boron to silicon within a range fromabout 3:100 to about 100:3 is that the obtained braze alloy will havewettability and thus good flow. Good flow is an advantage when brazingjoints because the obtained braze alloy will flow from the areas wherethe braze alloy is obtained and flow to the area of the joint. Thus, theobtained braze alloy layer on the substrate will have both flow and alower melting point compared to the parent material in the substrate.

According to a further example the method comprises applying a blend,wherein the blend is a mechanical blend. The blend could be a blend ofmixed powders. The particles in the powder may be either a boron sourceor a silicon source. A blend is defined as mechanical mixing of two ormore components. According to the first aspect a blend is a mechanicalblend/mixture of two or more powders, i.e. a blend of “silicon source”powder and “boron source” powder.

According to another example the method comprises that silicon and boronin the blend in step (i) may be present in the blend in at least 35 wt%, more preferred silicon and boron are present in the blend in step (i)in at least 40 wt %, most preferred in at least 45 wt %.

According to yet another example the method comprises that silicon andboron in the blend in step (i) may be present in the blend in at least50 wt %, more preferred silicon and boron are present in the blend instep (i) in at least 60 wt %, most preferred in at least 70 wt %, evenmore preferred in at least 80 wt %.

According to another example the method may comprise that the blend instep (i) may comprise boron and silicon in a weight ratio of boron tosilicon within a range from about 5:100 to about 1:1, preferably withina range from about 5:100 to about 2:1, more preferably the blend in step(i) may comprise boron and silicon in a weight ratio boron to siliconwithin a range from about 1:10 to about 7:10, most preferred the blendin step (i) may comprise boron and silicon in a weight ratio boron tosilicon within a range from about 15:100 to about 4:10.

According to another example the method comprises applying on thesubstrate a first layer of at least one boron source, and applying asecond layer of at least one silicon source on top of the first layer.

According to another example the method comprises applying a siliconsource, the silicon source is selected from one or more of elementalsilicon, an alloy containing silicon, or compound containing silicon.

According to a further example the method comprises method comprisesapplying a boron source, the boron source is selected from one or moreof elemental boron, an alloy containing boron, or compound containingboron.

According to a further example the method comprises applying a boronsource, the boron source is selected from elemental boron, boroncarbides, nickel borides, and silicon borides.

According to a further example the method comprises applying a siliconsource, the silicon source is selected from elemental silicon, ferrosilicon, iron silicides, silicon carbides, and silicon borides.

According to a further example the boron source and the silicon sourceare the same preferably silicon borides.

According to another example the blend may comprise that the boronsource may be selected from elemental boron, B₄C, B₄Si, B₃Si, NiB, andFeB, and the silicon source may be selected from elemental silicon,FeSi, SiC, and B₄Si, B₃Si.

According to another example the method comprises applying the blend asa powder, and the average particles size of the powder is <250 μm,preferably the average particle size <160 μm, most preferred theparticles having an average particle size <100 μm, most preferred theparticles having an average particle size less than 50 μm.

One advantage of a particle size less than 250 μm is the ability todistribute the blend as evenly as possible on the substrate.

According to another example the method may comprise that in step (i)the blend is comprised in a composition and that the composition furthercomprises at least one binder, said at least one binder may be selectedfrom the group consisting of solvents, water, oils, gels, lacquers,varnish, binders based on monomers and/or polymers.

According to another example the method may comprise that in step (i)the at least one binder may be a gel or a lacquer or a varnish.

According to another example the method may comprise that in step (i)the at least one binder may be selected from polyesters, polyethylene,polypropylene, acrylic polymers, met acrylic polymers, polyvinylalcohol, polyvinyl acetate, polystyrene.

According to a further example, the binder may be a polyester, a wax orcombinations thereof.

According to a further example, the composition is a paint or thecomposition is a paste or the composition is a dispersion.

According to a further example, the binder is a gel, and the compositionis a paste.

One advantage when the composition is a paste is that the paste easilycan be applied to selected areas on the substrate.

According to another example the method may comprise that in step (i)the composition may be a paint.

One advantage of a composition being a paint is that the paint easilycan be distributed over the surface of the substrate and adhere to thesurface and therefore can be handled during for instance transportation,pressing, cutting etc.

According to another example the method comprises applying a compositioncomprising the blend, at least one binder, and particles of a parentmaterial, and wherein the parent metal is present in an amount less than75 wt % calculated on the total weight of silicon, boron and parentmetal.

According to another example the composition may also comprise powdersof a parent material, wherein the parent material is present in anamount less than 75 wt % calculated on the total weight of silicon,boron and parent material. Such a composition provides for additionalparent material when obtaining the braze alloy during the alloyingprocess. When brazing for instance thin parts or thin plates additionalparent material can decreases or reduces the risk of burning through theplates or the parts, as seen in the Experimental Examples below.

According to further example the method comprises applying a compositioncomprising the blend, at least one binder, and particles of a brazingalloy.

According to further example the method comprises applying a substrateof a parent material selected from iron based alloys, nickel basedalloys, chromium based alloys, copper based alloys and cobalt basedalloys.

According to a further example the method may comprise that in step (i)the parent material may be an alloy comprising elements such as iron(Fe), chromium (Cr), nickel (Ni), molybdenum (Mo), manganese (Mn),copper (Cu), cobalt (Co) etc.

According to another example the method comprises applying a substrateof a parent material, said parent material comprises from about 15 toabout 22 wt % chromium, from about 8 to about 22 wt % nickel, from about0 to about 3 wt % manganese, from about 0 to about 1.5 wt % silicon,optionally from about 1 to about 8 wt % molybdenum, and balanced withiron.

According to another example the parent material comprises more than 50wt % Fe, less than 13 wt % Cr, less than 1 wt % Mo, less than 1 wt % Niand less than 3 wt % Mn.

According to example the parent material comprises more than 10 wt % Crand more than 60 wt % Ni.

According to another example the parent material comprises more than 15wt % Cr, more than 10 wt % Mo, and more than 50 wt % Ni.

According to another example the parent material comprises more than 10wt % Fe, 0.1 to 30 wt % Mo, 0.1 to 30 wt % Ni, and more than 50 wt % Co.

According to another example the parent material comprises more than 80wt % Ni.

According to another example the method comprises heating the substratehaving a surface layer of the applied blend or the applied compositionto a temperature higher than the melting point of an obtained moltenphase. The molten phase may be a brazing alloy and may have a liquidustemperature lower than the parent material.

According to another example the method comprises heating the substratehaving the applied blend or applied composition to a temperature higherthan 900° C. in the heating step.

According to another example the method comprises obtaining a moltenphase, the molten phase is obtained by alloying elements of the surfaceof the substrate with the blend in the heating step.

According to another example the method also comprises an additionalstep before step (i), said additional step comprises cutting or formingor combinations thereof of the metal substrate(s).

According to another example the method also comprises an additionalstep before the applying step or after the applying step or after theheating step, said additional step comprises cutting or forming orcombinations thereof of the product(s).

According to another example the method may comprise that the methodalso may comprise an additional step (iv), step (iv) comprises cuttingor forming or combinations thereof of the product(s) from step (iii).

According to another example the method according to any one of theexamples, wherein the substrate having the applied blend or the appliedcomposition is heated in step (ii) to temperatures within a range from900° C. to 1200° C.

The surface layer may be applied as a powder of the blend or by meanssuch as physical vapor deposition (PVD), or chemical vapor deposition(CVD). Physical vapor deposition (PVD) is a variety of vacuum depositionand is a general term used to describe any of a variety of methods todeposit thin films by the condensation of a vaporized form of thedesired film material onto various work-piece surfaces, e.g. ontosemiconductor wafers. The coating method involves purely physicalprocesses such as high temperature vacuum evaporation with subsequentcondensation, or plasma sputter bombardment rather than involving achemical reaction at the surface to be coated as in chemical vapordeposition. Chemical vapor deposition (CVD) is a chemical process usedto produce high-purity, high-performance solid materials. The process isfor example used in the semiconductor industry to produce thin films. Ina typical CVD process, the wafer, i.e. the substrate, is exposed to oneor more volatile precursors, which react and/or decompose on thesubstrate surface to produce the desired deposit. Frequently, volatileby-products are also produced, which are removed by gas flow through thereaction chamber.

According to another example the method according to any one of theexamples, wherein the method comprises obtaining plates, preferably heatexchanger plates, reactor plates, or parts of separators, decanters,pumps, valves etc. having a braze alloy layer.

The second aspect relates to a braze alloy layered product comprising asubstrate having at least one layer of a braze alloy, wherein thesubstrate comprises at least one parent material having a solidustemperature above above 1100° C., wherein the braze alloy layer has ahigher silicon content than the parent material and wherein the brazealloy layer has a melting point lower than the parent material.

According to one example the braze alloy layer has a content of at least2 wt % silicon.

According to a further example the braze alloy layer(s) has a Si-contentwithin a range from 2 wt % to 15 wt %.

According to a further example the braze alloy layer(s) has a Si-contentwithin a range from 2 wt % to 10 wt %.

According to a further example the braze alloy layer(s) has a Si-contentwithin a range from 5 wt % to 7 wt %.

According to another example the braze alloy layered product maycomprise that the braze alloy layer(s) may have a melting point lowerthan the parent material of the substrate.

According to a further example the braze alloy layered product hasferromagnetic properties for substrate of austenitic stainless steels.

According to another example the braze alloy layer has a thickness of atleast 5 μm.

According to another example the braze alloy layer has a thickness of atleast 10 μm.

According to another example the braze alloy layer has a thickness ofwithin the range from 5 μm to 120 μm, preferably within a range from 10μm to 110 μm.

According to a further example the solidus temperature of the parentmaterial may be above 1220° C. According to another example the solidustemperature of the parent material may be above 1250° C. According to afurther example the solidus temperature of the parent material may beabove 1300° C.

According to another example the braze alloy layered product hascompressive stress in the braze alloy layer on the substrate.

According to another example the substrate being one or more parts of aproduct to be joined, one or more plates to be joined, coils, partlybrazed objects.

According to a further example the braze alloy layered product has ahigher hardness in the braze alloy layer than in the parent material.Examples that the braze alloy layer has a higher hardness than theparent material can be seen in the Experimental Examples below.

The third aspect relates to a braze alloy layered product obtainable bythe method according to any one of the examples of the first aspect.

According to one example the braze alloy layered product obtainable bythe method according to any one of the examples of the first aspect, thebraze alloy layered product has the properties according to the examplesof the second aspect.

The forth aspect relates to a method for providing a brazed productcomprising the following steps:

Step (i) assembling at least one braze alloy layered product accordingto any one of the examples of the second aspect, with at least one metalsubstrates obtaining an assembled product or a stacked product;

Step (ii) heating the assembled or stacked product up to a temperaturebelow 1250° C. in a furnace in vacuum, in an inert gas, in a reducingatmosphere or combinations thereof; and

Step (iii) obtaining the brazed product with one or more joints at thecontact areas.

Contact areas refer to the areas where a first substrate is in contactwith a second substrate, and where a joint will be formed duringbrazing.

Assembling refers to stacking of for instance plates but not limited to,such as heat exchanger plates. Assembling refers further to assemblingof parts.

According to one example the method comprises that the obtained jointsare of similar material to the material as the parent material in thesubstrate(s).

According to a further example the method may comprise obtaining abrazed product provided with a joint(s) obtained at the contact pointsbetween the braze alloy layered product and another braze alloy layeredproduct or between the braze alloy layered product and anothernon-treated product of a substrate in a melting process, andtransferring a molten phase by capillary forces to the area of thecontact areas mainly from neighboring areas.

According to a further example the method also comprises cutting,forming, pressing or combinations thereof of the braze alloy layeredproduct.

According to a further example the obtained brazed product is selectedfrom heat exchangers, plate reactors, parts of reactors, parts ofseparators, parts of decanters, parts of pumps, parts of valves.

According to a further example the method may comprise cutting, forming,pressing or combinations thereof of the braze alloy layered productsprior to heating the assembled or stack the braze alloy layeredproducts.

The fifth aspect relates a brazed product obtained by the methodaccording to the forth aspect.

The sixth aspect relates a method for providing a coated productcomprising the following steps:

Step (i) applying wear resistant particles selected from one or more ofborides, nitrides, oxides, carbides, tungsten carbide, (cubic) boronnitride, titanium nitride, diamonds, metal composites, chromium boridesand combinations thereof on braze alloy layered products according toany one of the examples according to the second aspect;

Step (ii) heating the braze alloy layered product having the appliedwear resistant particles up to a temperature below 1250° C. in a furnacein vacuum, in an inert gas, in a reducing atmosphere or combinationsthereof; and

Step (iii) obtaining the coated product.

According to one example the coated product obtained by heating a brazealloy layered product according to the examples according to the secondaspect, to a temperature higher than the solidus temperature of theobtained brazing alloy, and lower than the solidus temperature of thesubstrate, obtaining a coated layer, preferably the coated layercomprises, surface enhancing particles, wear resistant particles orcatalyst, more preferred the coated layer comprises tungsten carbide,(cubic) boron nitride, titanium nitride, diamonds, metal composites,chromium borides.

According to one example the coated product may comprise particlesselected from hard particles or surface enhancing particle. Theparticles may be applied on the braze alloy layered product prior toheat treatment, and obtaining wear resistant surface or a surface whichhas an enhanced surface area.

A seventh aspect relates to a coated product obtained by the methodaccording to the sixth aspect.

A eight aspect relates to a use of a braze alloy layered productaccording to the examples according to the second aspect for brazing ofparts or products for heat exchangers, plate reactors, parts ofreactors, parts of separators, parts of decanters, parts of pumps, partsof valves.

A ninth aspect relates to a use of a braze alloy layered productaccording to any one the examples according to the second aspect forproducts having a hard surface.

In the brazed product obtained by the method the volume of the formedbrazing alloy is calculated from the following formula, see also FIG. 2:Volume=total area A×length of jointTotal area A=((X−B)/2)×((X−B)/2)×tan α

Wherein A is total area of the two triangles, X is the total width ofthe formed joint, B is the part of the formed joint where the volume ofthe formed brazing alloy in the center of the joint is negligible, andthe height is calculated by measuring the angle α, which is the angle ofthe between tangent of the pressed beam to the base.

Other embodiments and alternatives are defined by the claims.

In the following will the invention be explained by the use of FIGS. 1to 6. The figures are for the purpose of demonstrating the invention andare not intended to limit its scope.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is showing a circular pressed plate use in the Examples.

FIG. 2 is showing a graph of “Approximation”.

FIG. 3 is showing a diagram wherein the measured width as a function ofapplied amount (g/3500 mm²) with trend lines.

FIG. 4 is showing another diagram in which calculated filled area of thebraze joint based on the measured width as a function of applied amount(g/3500 mm²) with trend lines.

FIG. 5 is showing another diagram in which the % of the tensile testedsamples where the joint was stronger or the same as the than the platematerial as a function of applied amount of blend (gram per 3500 mm²)

FIG. 6 is showing picture of one of the samples after joining.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is showing a circular pressed plate, which is 42 mm in diameterand 0.4 mm thick, made of stainless steel type 316L. The pressed platehad two pressed beams V and H, each app 20 mm long. Beam V or v standsfor left beam and beam H or h stands for right beam, and v and h areused in Examples 5 and 9.

FIG. 2 shows approximation 1 which is based on a cross section of abrazed test sample. The cross section in FIG. 2 shows the pressed beamin the top of FIG. 2. In the bottom of FIG. 2 is the flat, earlierapplied plate. In the capillary between the beam and the flat surface ajoint is created. To estimate the amount of braze alloy created in thejoint following approximations and calculations have been made. It hasbeen estimated that the volume in the center of the joint is negligible.Therefore, the created braze alloy volume for joints with a width, i.e.width B of 1.21 mm or less, are set to zero. On the outer sides of thebeam, i.e. ((X−B)/2), formed braze alloy has been accumulated. Thus, thebrazing alloy in melted form has been transported by capillary forces tothe area of the joint mainly from neighboring areas forming the volumesbraze alloy of the triangles.

According to FIG. 2, it is possible to calculate an area by estimatethat two triangles are formed on each side of the centre of the joint.The angle in the triangle is measured to app. 28°. The total measuredwidth is called X and the center width, B. The total area (A) of the twotriangles are therefore A=2×(((X−B)/2)×((X−B)/2)×tan(α)))/2, i.e. forFIG. 2 A=2×(((X−1.21)/2)×((X−1.21)/2)×tan(28)))/2. The total createdvolume of braze alloy, which had flown to the crevices, would be thearea times the length of the two beams. Some of the formed braze alloydoes not flow to the crevices and is left on the surface. FIG. 3 isshowing a diagram wherein the measured width as a function of appliedamount (g/3500 mm²) with trend lines. The results of the fillet test areshown in table 8 and 9 of Example 5 and in FIG. 3. The trend lines ofFIG. 3 are base on Y=K×X+L. The results of the measured widths and theestimated areas are illustrated in the diagrams of FIG. 3. The appliedamounts, see Tables 8 and 9, were from 0.06 gram/3500 mm² to 0.96gram/3500 mm², which correspond to from app 0.017 mg/mm² to 0.274mg/mm², to be compared with app 1.3-5.1 mg of blend per mm² used inExample 2.

The trend line Y=K×X+L for the blend were measured, Y is the jointwidth, K is the inclination of the line, X is the applied amount ofblend and L is a constant, see FIG. 3. Thus, the width of braze joint:Y(width for A3.3)=1.554+9.922×(applied amount of blend A3.3)Y(width for B2)=0.626+10.807×(applied amount of blend B2)Y(width for C1)=0.537+8.342×(applied amount of blend C1)Y(width for F0)=0.632+7.456×−(applied amount of blend F0)

As observed from FIG. 3 blends A3.3 out of blends A3.3, B2, C1, D0.5,E0.3 and F0 give the highest amount of braze alloy in the joint as afunction of applied amount of blend. Sample F0 did not give anysubstantial joints below 0.20 gram per 3500 mm².

FIG. 4 is showing another diagram in which calculated filled area of thebraze joint based on the measured width as a function of applied amount(gram/3500 mm²) with trend lines. The trend line Y=K×X−L for the blendwere measured, Y is the area, K is the inclination of the line, X is theapplied amount of blend and L is a constant, see FIG. 4.Y(area for A3.3)=4.361×(applied amount of blend A3.3)−0.161Y(area for B2)=3.372×(applied amount of blend B2)−0.318Y(area for C1)=2.549×(applied amount of blend C1)−0.321Y(area for F0)=0.569×(applied amount of blend F0)−0.093

A rough estimation on the created volume based on the diagram in FIG. 4for e.g. an amount of 0.18 gram per 3500 mm², excluding sample F0, dueto “no” braze joints and sample D0.5 due to too little data, gives avalue for the samples for created volume of braze alloy in the jointbetween the two beams, see below.Volume(A3.3)=0.63×length 40(20×2)=25.2 mm³Volume(B2)=0.30×length 40(20×2)=12.0 mm³Volume(C1)=0.12×length 40(20×2)=4.8 mm³Volume(E0.3)=0.10×length 40(20×2)=4.0 mm³

FIG. 5 is showing another diagram in which the % (percent) is thesuccess rate of the tensile tested samples where the joint was strongeror the same as the plate material as a function of applied amount ofblend, i.e. gram per 3500 mm². When the plate was stronger than thejoint, resulting in a split of the joint, the result was set to zero.For the samples that the joint were stronger than the plate material thedifference in results was not statistical significant.

In the picture of FIG. 6 is one of the samples shown after joining. Thepicture shows that there is a formed joint between the two pieces. Thejoined sample is from Example 10.

The invention is explained in more detail in by means the followingExamples and the Examples are for illustrating the invention and are notintended to limit the scope of invention.

EXAMPLES

The tests in these Examples were made to investigate if silicon, Si, isable to create a braze alloy when applied on the surface of a testsample of base metal. Also different amounts of boron, B, were addedsince boron can decrease the melting point for braze alloys. Boron canalso change the wetting behavior of braze alloys. Properties of thetested blends were also investigated. In the Examples wt % is percent byweight and atm % is percent of atoms.

If nothing else is stated the test samples of parent metal for all testswere cleaned by dish washing and with acetone before samples of theblends of silicon and boron were added to the test samples.

Example 1: Preparation of Blends of Silicon and Boron to be Tested

Test sample No. C1 was prepared by blending 118.0 gram of crystallinesilicon powder particle size 325 mesh, 99.5% (metal basis) 7440-21-3from Alfa Aesar-Johnsson Matthey Company, with 13.06 gram of crystallineboron powder particle size 325 mesh, 98%, 7440-42-8 from AlfaAesar-Johnsson Matthey Company and 77.0 gram of Nicrobraz S-30 binderfrom Wall Colmonoy in a Varimixer BEAR from Busch & Holm producing 208gram of paste, see sample C1. All test samples were produced followingthe same procedure as test sample C1. The blends are summarised in Table3.

TABLE 3 Sample Boron Silicon S-30 Binder Total Weight No. [gram] [gram][gram] [gram] F0 0.00 124.7 73.3 198 E0.3 4.30 123.9 72.1 200 D0.5 6.41121.2 75.0 203 C1 13.06 118.0 77.0 208 B2 24.88 104.5 72.81 202 A3.311.46 22.9 19.3 54.0

Samples G15, H100, I66 and J was prepared the same way as samples F0,E0.3, D0.5, C1, B2 and A3.3 with the exception that another binder wasused, the binder was Nicrobraz S-20 from Wall Colmonoy. The test samplesare summarised in Table 4.

TABLE 4 Sample Boron Silicon S-20 Binder Total Weight No. [gram] [gram][gram] [gram] G15 0.37 2.24 3.1 5.7 H100 4.19 0 5.3 9.5 I66 1.80 2.705.5 10.0 J 2.03 2.02 5.0 9.0

The samples are also calculated to show ratio, percent by weight andpercent by atoms, these are shown in Table 5.

TABLE 5 Blend Ratio Amount Amount Sample [wt/wt] [wt %] [atm %] No.Boron Silicon Boron Silicon Boron Silicon F0 0 100 0 100 0 100 E0.3 3100 3 97 8 92 D0.5 5 100 5 95 12 88 C1 10 100 9 91 21 79 B2 19 100 16 8433 67 A3.3 33 100 25 75 46 54 G15 17 100 14 86 30 70 H100 100 0 100 0100 0 I66 66 100 40 60 63 37 J 100 100 50 50 72 28Measure of Binder (Polymeric and Solvent) Content in the S-20 and S-30Binder.

Also the content of “dry” material within the gels was tested. Samplesof S-20 and S-30 were weighted and thereafter placed in an oven for 18hours at 98° C. After the samples had been taken out of the oven theywere weighted again. The results can be found in Table 6.

TABLE 6 Polymeric Before After fraction Sample [gram] [gram] [wt %] S-20199.64 2.88 1.44 S-30 108.38 2.68 2.47

Example 2: Brazing Tests

When testing the flow and wetting characteristics for braze fillers ofthe prior art, the weight of the applied braze filler is 2.0 gram whichcorrespond to 0.2 gram of silicon. Since blends of silicon and boronwere to be tested similar amounts of silicon and boron in the testedcompositions were used. The braze filler contains 10 wt % silicon,therefore 0.2 gram of blends of silicon and boron were applied on thetest samples. The test samples were circular test pieces having adiameter of 83 mm and a thickness of 0.8 mm and the test pieces weremade of stainless steel type 316L. Since it was not expected that 0.2gram of blend (Si and B) would correspond to 2 gram of braze alloybecause a “formed braze alloy” must first be created from the parentmetal and Si and B. Therefore, a higher amount, i.e. 0.4 gram was alsotested. The behavior of “formed braze alloy” was tested for ability toflow, if the “formed braze alloy” would not flow, then would silicon andboron only diffused into the base metal or even not melt the base metal?All samples were brazed in a vacuum furnace at 1210° C. for 1 hour.Double tests were used. Meaning, two weights 0.2 gram and 0.4 gram,double test samples and six different blends i.e. F0, E0.3, D0.5, C1, B2and A3.3, adding up to 2×2×6=24 samples. The blends were applied on acircular area having a diameter of app 10 to 14 mm, i.e. a surface of 78to 154 mm² or app 1.3-5.1 mg of blend per mm².

Results

It was clearly observed that the test pieces of the base metal hadmelted and some type of melts were created. It was also observed thatthe melts in some aspects appeared as a braze alloy with flow. Withoutmeasuring the size of the wetting it was clear that an increasedfraction of boron in the blends resulted in better wetting. However itwas also seen that for most samples the entire thickness of the coveredarea had melted creating a hole was created in the middle of the testpiece. For the “0.2 gram samples” five out of twelve test pieces hadholes, and for the “0.4 gram pieces” ten out of twelve.

One conclusion is therefore that it is not possible to change from abraze filler paste or the like and apply spots or lines with“comparative equal amounts” of blends of silicon and boron, since theblends of silicon and boron will melt a hole in the base metal if thetest sample is thin, in this case 0.8 mm. If thicker test samples areused no holes might appear, but, “grooves” might be created in the basemetal. This could be prevented or be improved by adding parent metal ase.g. powder to the silicon and boron blends. If only silicon is applied,i.e. sample F0, the result appear to have less flow and wettingproperties than the other samples wherein both silicon and boron areapplied.

Example 3: New Applying Procedure

In this Example the test plates were prepared for all fillet tests,corrosion tests and tensile tests at the same time. From Example 2 itwas concluded that it could be a risk to apply the blends of silicon andboron in dots or lines on thin walled plates. Therefore, new testssamples were investigated, i.e. new test plates were applied withdifferent blends of Si and B for fillet tests, corrosion tests, andtensile tests.

Accordingly, the new test samples were plates made of stainless steeltype 316L. The size of the plates were 100 mm wide, 180 to 200 mm longand the thickness was 0.4 mm. All plates were cleaned by dish washingand with acetone before application of the Si and B blends. The weightwas measured. On each plate a 35 mm section at one short side wasmasked.

The different blends used were A3.3, B2, C1, D0.5, E0.3, F0, G15, H100,and I66, all with the added binder S-30. The plates were “painted” withthe blends on the unmasked surface area, which surface area had the sizeof 100 mm×35 mm. After drying for more than 12 hours in room temperaturethe masking tape was removed and the plate weight was measured for eachplates. The weight presented in Table 7 below is the eight of thetotally amount of the blends on the area of 100 mm×35 mm=3500 mm²=35cm².

TABLE 7 Weight of blend Weight of Si + B Ratio blend + dried withoutWeight of Samples B:Si binder binder blend per area No. [wt/wt] [gram][gram] [mg/cm²] A3.3 33:100 0.0983 0.0959 2.74 B2 19:100 0.0989 0.09652.76 C1 10:100 0.1309 0.1277 3.65 D0.5  5:100 0.1196 0.1166 3.33 E0.3 3:100 0.0995 0.0970 2.77 H100 100:0   0.1100 0.1073 3.07 I66 66:1000.0900 0.0878 2.51

Example 4: Corrosion-Bend Test of the Samples

The test plates from Example 3 were cut to 35 mm wide strips, resultingin an applied surface area of 35 mm×35 mm on each strip. A circularpressed plate was placed onto the surface areas of the strips. Thecircular pressed plate is shown in FIG. 1. The pressed plate had a sizeof 42 mm in diameter and 0.4 mm thick and was of stainless steel type316L. The test samples were brazed 1 hour at 1210° C. The specimensprepared for the corrosion tests were applied with blend samples A3.3,B2, C1, D0.5, E0.3, H100, I66 and J, see Table 5.

The specimens were tested according to corrosion test method ASTM A262,“Standard Practices for Detecting Susceptibility to inter-granularAttack in Austenitic Stainless Steels”. “Practice E—Copper—CopperSulfate—Sulfuric Acid. The test for Detecting Susceptibility toInter-granular Attack in Austenitic Stainless Steels”, was selected fromthe test method. The reason for selecting this corrosion tests was thesuspicion that boron might react with chromium in the steel creatingchromium borides, mainly in the grain boundaries, which increase therisk for inter-granular corrosion attack. The specimens were placed inboiling 16% sulfuric acid together with copper sulfate in 20 hours, whatin the standard is referred to as “practice” and thereafter a bend test,according to chapter 30 in the standard.

Results from the Corrosion Test and Sectioning of the Test Samples

The test pieces were bend tested according to the corrosion test methodin chapter 30.1. None of the samples gave indications of inter-granularattack at the ocular investigation of the bent surfaces. After the ASTMinvestigation the bent specimens were cut, ground and polished and thecross-sections were studied in light optical microscope and in EDS, i.e.Energy Dispersive Spectroscopy. The results are summarized in Table 8.

TABLE 8 Ocular investigation of surface for corrosion cracks when bentResults of metallurgical experimentation of according thecross-sectioned corrosion tested Sample to the samples and bend testedtest samples. No. ASTM test SEM-EDS results A3.3 No cracks No corrosionA surface layer of app. max 8 μm with a few cracks. The phase that hadcracked had a high Cr and B content, most probably due to Cr—Bprecipitates B2 No cracks No corrosion A surface layer of app. max 8 μmwith a few cracks. The phase that had cracked had a high Cr and Bcontent, most probably a chromium boride phase C1 No cracks No corrosionor cracks D0.5 No cracks No corrosion or cracks E0.3 No cracks Nocorrosion A surface layer of app. max 60 μm with a few cracks. The phasethat had cracked had a high Si content generally <5 wt % H100 No cracksCorroded surface and joint I66 No cracks No corrosion A surface layer ofapp. max 12 μm with a few cracks. The phase that had cracked had a highCr and B content, most probably a chromium boride phase J No cracks Nocorrosion A surface layer of app. max 20 μm with a few cracks. The phasethat had cracked had a high Cr and B content, most probably a chromiumboride phase

Comments

Apparently when adding high amounts of boron, as for sample H100, J,I66, a brittle layer is formed on the surface. The layer is likely dueto a high concentration of chromium boride precipitates, increasing withthe amount of boron. No brittle layer was found in the H100 sample, mostprobably due to the corrosion on the surface. As the amount of chromiumborides is increased with increased amount of boron, it also has to betaken into consideration that the corrosion properties might decrease.This would explain why sample H100 that was attacked in the corrosiontest. The “negative” effect of boron can be decreased by using thickersubstrates and/or longer diffusion times. It is then possible to“dilute” boron by diffusing it into the parent metal. For the smalleramount of boron samples A3.3 and B2, a thinner brittle surface layer wasformed. It was seen that for the low amount of boron sample E0.3, aquite thick brittle surface layer, with a high silicon contentgenerally >5 wt % of silicon, was formed. This layer had differentcharacteristics than the brittle surfaces for A3.3, B2, H100, I66 and J.“The negative” effect with silicon can be decreased by using thickerbase metals and/or longer diffusion times. It is then possible to“dilute” silicon in the base metal.

Example 5: Fillet Test of the Samples

The test plates from Example 3 were cut to 35 mm wide strips, resultingin an applied surface area of 35 mm×35 mm on each strip. A circularpressed plate was placed onto the surface areas of the strips. Thecircular pressed plate is shown in FIG. 1. The pressed plate had a sizeof 42 mm in diameter and 0.4 mm thick and was of stainless steel type316L. The pressed plate had two pressed beams, each app 20 mm long. Thesamples were brazed at app 1 hour at app 1200° C.

The results from the fillet test show the width of the braze alloy foundin the joint area created between the flat surface area and the contactwith a pressed beam in the test sample seen in FIG. 1. The blends wereapplied onto the flat surface areas before heating. The amount of brazealloy was estimated; see FIG. 2, by an approximation of the area of thefillet cross-section to two triangles formed on each side of the centerof the joint. In the middle part there are no or very small amounts ofadditional formed “brazing alloy”. The area of the two triangles can becalculated by measuring the height (h) and the base (b). The total areaof the two triangles are summing up to (h)×(b) since there are twotriangles. The problem with this calculation is that the height is hardto measure. Therefore we use the following equation for calculating ofthe two triangle areas:A=((X−B)/2)×((X−B)/2)×tan α

A is the total area of the two triangles, X is the total width of theformed joint, B is the part of the formed joint where the volume of theformed brazing alloy in the center of the joint is negligible. Thus, thebase of each triangle is (X−B)/2. The height is calculated by measuringthe angle α, which is the angle between the tangents of the pressed beamthe base plate.

To calculate the volume of the total created volume of the formed brazealloy that had flowed to the crevices, the length of the two beams, i.e.each beam is 20 mm, was multiplied with A.

The area of two triangles is the estimated area after brazing in Table 9and 10. The volume is the volume of the formed brazing alloy on one ofthe beams. The results from the fillet test are shown in Table 9 and 10,and in FIG. 3. In Table 9 and in Table 10 v and h stand for v=left beamand h=right beam.

TABLE 9 Applied binder Estimated Area Sample Si + B Width after brazingVolume No. [gram] [mm] [mm²] [mm³] A3.3x-1v 0.06 2.69 0.29 5.8 A3.3x-1h0.06 2.58 0.25 5.0 A3.3-1v 0.10 2.23 0.14 2.8 A3.3-1h 0.10 2.31 0.16 3.2A3.3-2v 0.14 3.38 0.63 12.6 A3.3-2h 0.14 3.19 0.52 10.4 A3.3-3v 0.091.92 0.07 1.4 A3.3-3h 0.09 1.85 0.05 1.0 B2X-1v 0.18 2.12 0.11 2.2B2X-1h 0.18 2.50 0.22 4.4 B2X-2v 0.15 2.31 0.16 3.2 B2X-2h 0.15 2.310.16 3.2 B2-1v 0.10 1.96 0.07 1.4 B2-1h 0.10 1.92 0.07 1.4 B2-2v 0.243.23 0.54 10.8 B2-2h 0.24 3.23 0.54 10.8 B2-3v 0.16 2.77 0.32 6.4 B2-3h0.16 2.69 0.29 5.8 B4v 0.11 1.35 0.00 0 B4h 0.11 1.35 0.00 0 Fillet testresults, samples A3.3-B2/B4

TABLE 10 Applied binder Estimated Area Sample Si + B Width after brazingVolume No. [gram] [mm] [mm²] [mm³] C1X-1v 0.22 2.50 0.22 4.4 C1X-1h 0.222.69 0.29 5.8 C1X-2v 0.33 3.08 0.46 9.2 C1X-2h 0.33 3.27 0.56 11.2 C1-1v0.13 1.46 0.01 0.2 C1-1h 0.13 1.46 0.01 0.2 C1-2v 0.15 1.96 0.07 1.4C1-2h 0.15 2.08 0.10 2.0 C1-3v 0.14 1.54 0.01 0.2 C1-3h 0.14 1.62 0.020.4 D0.5-1v 0.19 2.54 0.23 4.6 D0.5-1h 0.19 2.50 0.22 4.4 D0.5-2v 0.121.08 0.00 0 D0.5-2h 0.12 1.08 0.00 0 D0.5-3v 0.14 2.04 0.09 1.8 D0.5-3h0.14 2.04 0.09 1.8 E0.3-1v 0.13 1.15 0.00 0 E0.3-1h 0.13 1.15 0.00 0E0.3-2v 0.21 2.31 0.16 3.2 E0.3-2h 0.21 2.31 0.16 3.2 E0.3-3v 0.10 1.350.00 0 E0.3-3h 0.10 1.35 0.00 0 F0-1h 0.45 2.69 0.29 5.8 F0-2v 0.25 1.080.00 0 F0-2h 0.25 1.35 0.00 0 F0-3v 0.96 2.96 0.41 8.2 F0-3h 0.96 3.080.46 9.2 Fillet test results samples C1 to F0

The results of the measured widths and the estimated areas are presentedin the Tables 9 and 10, and illustrated in the diagrams of FIG. 3. Theapplied amounts, see Tables 9 and 10, varied from 0.06 gram/3500 mm² to0.96 gram/3500 mm². This corresponds to from approx. 0.017 mg/m² to0.274 mg/mm², to be compared with approx. 1.3-5.1 mg of blend per mm²used in Example 2.

The trend lines Y=K×X+L for the blends were calculated. Y is the jointwidth [mm], K is the inclination of the line, X is the applied amount ofblend [g] and L is a constant, see FIG. 3. Thus, the width of brazejoint:Y(width for A3.3)=1.554+9.922×(applied amount of blend A3.3)Y(width for B2)=0.626+10.807×(applied amount of blend B2)Y(width for C1)=0.537+8.342×(applied amount of blend C1)Y(width for F0)=0.632+7.456×−(applied amount of blend F0)

As observed from the diagram, blend A3.3 out of blends A3.3, B2, C1,D0.5, E0.3 and F0 gives the highest amount of braze alloy in the jointas a function of applied amount of blend. Sample F0 did not give anysubstantial joints below 0.20 gram per 3500 mm².

The trend line Y=K×X−L for the blend were measured, Y is the area [mm²],K is the inclination of the line, X is the applied amount of blend [g]and L is a constant, see FIG. 4.Y(area for A3.3)=4.361×(applied amount of blend A3.3)−0.161Y(area for B2)=3.372×(applied amount of blend B2)−0.318Y(area for C1)=2.549×(applied amount of blend C1)−0.321Y(area for F0)=0.569×(applied amount of blend F0)−0.093

A rough estimation on the created volume based on the diagram in FIG. 4for e.g. an amount of 0.18 gram per 3500 mm², excluding sample F0, dueto “no” braze joints and sample D0.5 due to too little data, gives avalues for the samples for created volume of braze alloy in the jointbetween the two beams, as seen below.Volume(A3.3)=0.63×length 40(20×2)=25.2 mm³Volume(B2)=0.30×length 40(20×2)=12.0 mm³Volume(C1)=0.12×length 40(20×2)=4.8 mm³Volume(E0.3)=0.10×length 40(20×2)=4.0 mm³

Also blends with a higher fraction of boron were tested e.g. G15, H100,I66 and J. All these blends did work quite similar to blend A3.3 and B2regarding the created braze alloy volume. However, the metallurgicalcross section of the brazed samples showed that the amount of borideswas greater. For sample H100, i.e. pure boron, also brittle highchromium phases were found on the surface where the blend earlier wasapplied. The hard phases were most probably chromium borides, whichlower the chromium content in the surrounding material, therebydecreasing the corrosion resistance. This may be an issue when goodcorrosion resistance is wanted but is not an issue for non-corrosiveenvironment. The effect of boron could be decreased by changing the heattreatment and or by using a thicker base metal that can “absorb” agreater amount of boron. For a thicker material, i.e. ≥1 mm, this effectto “absorb” boron in the surface will also be less severe, since theproportion of the surface volume compared to the parent metal volume ismuch less than for a thin material <1 mm or <0.5 mm. The chromiumborides could be an advantage if better wear resistance is wanted. Themetallurgical investigation also showed that for sample F0, i.e. puresilicon, a thick brittle layer containing a silicon phase was found.This layer had a thickness of >50% of the plate thickness for some areasin the investigated sample. The similar phase was also found in thejoint. Cracks were found in this phase, with a length >30% of the platethickness. Such cracks will decrease the mechanical performance of thejoined product and can be initiating points for corrosion and/or fatiguecracks. The average measured hardness of the phase was over 400 Hv(Vickers). This brittle phase is probably much harder to decrease,compared to the boride phase, by using thicker base metal or a change inheat treatment. Still for thicker base metal this effect can be lesssevere.

Example 6: Tensile Test of Brazed Joint

The original applied test plates were cut into strips. The size of theplate was approx. 100 mm wide, 180 to 200 mm long and the thickness 0.4mm. The applied area for each strip was 10 mm by 35 mm=350 mm². Athicker part, 4 mm, of stainless steel type 316L was placed on theapplied area covering 30 mm of the total 35 mm applied surface. Theticker part was placed at the end of the strip leaving 5 mm of appliedsurface not covered by the thick plate. By doing this a decrease in theplate material strength due to the applied blend would be detected bytensile testing, if the joint is stronger than the plate. The thickerplate was also wider than the 10 mm slices. All test samples were brazedat approx. 1200° C. for approx. 1 hour.

After brazing, a 90° peel test was carried out and the thick part oftest sample was mounted horizontally to the bottom part in a tensiletest machine. The braze strip was firmly bent 90°, to a verticaldirection and the strip was mounted to the top part of the tensile testmachine. The thick part of the test samples was mounted so that it couldmove in horizontal direction. The samples were then loaded and the brazejoint were split or the strip failed/cracked.

Results

The results are presented as the (%) fraction of non-failed joints foreach condition The test failed if the plate was stronger than the joint,which resulted in that the joint were split. If the joint was strongerthan the plate (the non-failed condition), the plate cracked/failedbefore the joint. The results are summarized in Table 11 and in thediagram of FIG. 5.

TABLE 11 Blend of A3.3-1 B2-1 C1-1 D0.5-1 Si + B Success Rate SuccessRate Success Rate Success Rate [gram] [%] [%] [%] [%] 0.0600 100 0.0910100 0.0989 83 0.1092 100 0.1196 0 0.1309 50 0.1399 100 0.1402 50 0.14280 0.1500 100 0.1548 67 0.1558 100 0.1800 100 0.1850 50 0.2200 100 0.2417100 0.3000 100 0.3300 100

Example 7

To establish the relationship between applied amount and the risk forburning holes through the plates, as described in Example 2, new testswere performed. For all tests blend B2, see Table 6, was used. To blendB2 binder S-30 was added. The test pieces were circular stainless steeltype 316 with a thickness of 0.8 mm and a diameter of 83 mm. For allsamples the blend was applied in the center of the test piece. Theapplied area was 28 mm², i.e. circular spot having a diameter of 6 mm.All test samples were weighed before and after application, and theresults are summarized in Table 12. Thereafter the test samples wereplaced in room temperature for 12 hours. The samples were weighed again.

The test samples were all put in a furnace and were brazed at 1210° C.for approx. 1 hour. During brazing only the outer edges of each samplewere in contact with the fixture material, keeping the plate centerbottom surface free from contact with any material during brazing. Thereason for keeping the plate center bottom surface free from contacts isthat a collapse or a burn through might be prevented if the centermaterial is supported from below by the fixture material.

Applied amount and burn through results for the 0.8 mm samples aresummarized in Table 12.

TABLE 12 Blend of Calculated Blend of Si + B and Blend of amount of Si +B and additional Si + B and Blend of additional wet additional Si + Bwet binder dried without Burn Sample binder S-30 S-30 binder S-30 binderthrough No. [gram] [mg/mm²] [mg/mm²] [mg/mm²] [1] or [0] 1 0.020 0.7140.464 0.453 0 2 0.010 0.357 0.232 0.226 0 3 0.040 1.429 0.928 0.905 0 40.030 1.0714 0.696 0.679 0 5 0.050 1.786 1.161 1.132 0 6 0.060 2.1431.393 1.359 0 7 0.070 2.500 1.625 1.585 0 8 0.080 2.857 1.857 1.811 0 90.090 3.214 2.089 2.037 0 10 0.100 3.571 2.321 2.264 0 11 0.110 3.9282.554 2.491 1 12 0.120 4.285 2.786 2.717 1 13 0.130 4.642 3.018 2.943 114 0.150 5.357 3.482 3.396 1 15 0.170 6.071 3.946 3.849 1 16 0.190 6.7864.411 4.302 1 17 0.210 7.500 4.875 4.755 1 18 0.230 8.214 5.339 5.207 119 0.280 10.000 6.500 6.339 1 20 0.290 10.357 6.732 6.566 1

The tests show that sample 11 has a burn through. Sample 10 has 2.264mg/mm² applied amount of blend and sample 11 has 2.491 mg/mm². Forjoining plates having thickness less than 1 mm, there is a risk with anamount within the range from about 2.830 mg/mm² to about 3.114 mg/mm²for burning through the plates, the amount in the middle of this rangeis 2.972 mg/mm². Therefore, for a plate having a thickness less than 1mm an amount of less than 2.9 mg/mm² would be suitable for avoidingburning through the plate. The result also show that 2.491 mg/mm² willburn through a plate which is less thick than 0.8 mm and have circularspot having a diameter of 6 mm applied with the blend. For samples withsmaller applied areas may have more applied blend per area than sampleswith larger applied areas.

Example 8

In Example 8 a braze joint between two pressed heat exchanger plates ismade by three different ways. The thickness of the heat exchanger platesare 0.4 mm.

In the first and second test samples an iron based braze filler with acomposition close stainless steel type 316 was used, see WO 2002/38327.The braze filler had a silicon concentration of about 10 wt %, boronconcentration about 0.5 wt % and a decreased amount of Fe of about 10.5wt %. In the first test sample the braze filler was applied in lines andin the second test sample the braze filler was applied evenly on thesurface. In both cases the filler was applied after pressing.

After brazing test sample 1 showed that the braze filler applied inlines was drawn to the braze joints. Some of the braze filler did notflow to the braze joint and therefore increased the thickness locally atthe applied line. For test sample 2 the braze filler flowed to the brazejoints, however some on the braze filler remained on the surface andincreased the thickness. In both test samples, 1 and 2, the amount ofadded braze filler corresponded to approx. 15 wt % of the platematerial.

In test sample 3, A3.3 blend was used, see Table 7. The blend wasapplied evenly on the plate before pressing. The blend was applied in anamount that would create braze joint with similar sizes as for testsamples 1 and 2.

Test sample 3 was applied with an even layer of A3.3. This amountcorresponds to a weight ratio blend:plate material of about 1.5:100.When brazing, a braze alloy was formed mainly from the parent metal.This braze alloy flowed to the braze joints. Accordingly, the thicknessof the plate decreased since the parent material was dissolved and drawnto the braze joints.

Example 9: Tests with Different Si-Sources and B-Sources

The tests in Example 9 were done to investigate alternativeboron-sources and silicon-sources. Blend B2, see Table 7, was selectedas reference for the test. The alternative sources were tested withtheir ability to create a joint. For each experiment either analternative boron-source or an alternative silicon-source was tested.When using an alternative source the influence of the secondary elementwas assumed to be zero, meaning that it was only the weight of boron orsilicon in the alternative component that was “measured”, see Table 13.For the reference blend B2, the weight ratio between silicon and boronis 10 to 2. Each blend was mixed together with S-30 binder and the blendwas applied on a steel plate according to Example 1. All samples werebrazed in a vacuum furnace at 1210° C. for 1 hour.

TABLE 13 Added Correspond- Amount Added ing Corre- Si- Amount Amountsponding Alternative source B-source Si Amount B Sample source [gram][gram] [gram] [gram] Si—B Si—B 10.0 2.0 10.0 2.0 Si—B₄C B₄C 10.0 2.610.0 2.0 Si—FeB FeB 10.1 12.5 10.1 2.0 FeSi—B FeSi 30.2 2.0 10.1 2.0Si—NiB NiB 10.1 13.0 10.1 2.0

The trend line Y=K×X+L for blend B2 was measured, Y is the joint width[mm], K is the inclination of the line for B2, X is the applied amountof blend [g] and L is a constant for no applied amount of blend B2, seeFIG. 3. Thus, the width of braze joint Y=0.626+10,807×(applied amount ofblend).

In Table 14 v and h stand for l=left beam and r=right beam as in Example5.

TABLE 14 Joint Applied Joint Measured Amount Calculated Width Y WidthSample [gram] [mm²] [mm²] Si—B₄C-l 0.22 3.0 2.69 Si—B₄C-r 0.22 3.0 2.88Si—FeB-l 0.26 3.4 1.73 Si—FeB-r 0.26 3.4 1.73 FeSi—B-l 0.29 3.8 2.1FeSi—B-r 0.29 3.8 2.1 Si—NiB-l 0.39 4.8 2.69 Si—NiB-r 0.39 4.8 2.88

The results in Table 13 show that it is possible to use B₄C, NiB and FeBas alternatives source to boron. When NiB was used, the created amountof braze alloy was less than for pure boron, however, NiB could be usedif an Ni alloying effect is wanted.

Example 10: Tests of Base Metals

In Example 10 a large number of different base metals were tested. Alltests except for the mild steel and a Ni—Cu alloy were tested accordingto test Y.

For test Y two circular pressed test pieces with a thickness of app 0.8mm were placed onto each other. Each sample had a pressed circular beam.The top faces of the beams were placed towards each other creating acircular crevice between the pieces. For each sample the B2 blend withbinder S-20 were applied with a paint brush. The weight of the addedamount was not measured since the purpose with the test was toinvestigate if was possible to create a braze filler and not test howdifferent amounts affected the results. A picture of one of the samplesafter joining is presented in FIG. 6.

The blend was applied to the mild steel samples and the Ni—Cu samples inthe same way. For mild steel the tests made were performed as in example5 “fillet test”. The Ni—Cu test was performed with two flat test pieces.All samples except for the Ni—Cu were “brazed” in a furnace at approx.1200° C., i.e. 1210° C., for 1 h in vacuum furnace. The Ni—Cu sample wasbrazed at approx. 1130° C. for approx. 1 h in the same vacuum furnace.After “brazing” a joint had formed between the pieces for all madetests. A flow of created “braze alloy” manly consisting of the parentmetal, to the joint was also observed for all tested samples. Theresults are shown in Table 15.

TABLE 15 After Parent After Brazing material Cr Fe Mo Ni Cu Mn BrazingFlow of Sample [wt [wt [wt [wt [wt [wt Created Brazing No. %] %] %] %]%] %] joint? Alloy? 1 — 0.3 — 99 — 0.2 Yes Yes 2 21 0.6 16 62 0.4 — YesYes 3 22 0.7 16 59 1.6 — Yes Yes 4 0.6 1.9 29 68 0.2 — Yes Yes 5 21 4.413 58 — — Yes Yes 6 19 5.0 9.0 63 0.4 — Yes Yes 7 15 5.5 17 60 — 0.3 YesYes 8 1.1 5.6 28 63 0.6 0.4 Yes Yes 9 19 6.2 2.6 70 1.7 0.4 Yes Yes 1033 32 1.7 33 0.4 0.6 Yes Yes 11 27 33 6.5 32 1.1 1.4 Yes Yes 12 27 363.4 32 1.0 1.4 Yes Yes 13 24 44 7.2 23 0.3 1.5 Yes Yes 14 20 48 4.3 251.1 1.2 Yes Yes 15 19 50 6.3 25 0.2 — Yes Yes 16 20 54 6.5 19 0.6 0.4Yes Yes 17 29 64 2.4 3.5 — — Yes Yes 18 28 66 2.2 3.5 — — Yes Yes 19 0.31.1 — 66 31 1.6 Yes Yes 20 0.17 99.5 — — — 0.3 Yes Yes

The results in Table 15 show that braze alloys are formed between theblend and the base metal for each sample 1 to 20. The results also showthat joints were created for each tested sample.

The results from examples 1 to 10 show that boron was needed to create asubstantial amount of braze alloy, which could fill the joints and alsocreate strength in the joints. The examples also show that boron wasneeded for the microstructure, since a thick brittle layer was formed onthe samples with no boron.

Example 11: Pre-Brazing Tests

Four different parent materials were tested in Example 11. The blendthat was used for the test pieces was blend A3.3, see earlier Examples.All blends were made using Si and B as melting point depressant sources,dispersed in a lacquer from Akzo Nobel (if nothing else stated). Theparent material of the test pieces were:

1. Stainless Steel type 316 thickness 0.4 mm

2. Ni type 200 thickness 0.45 mm

3. Monel 400 thickness 1.0 mm

4. Hastelloy C2000 thickness 0.5 mm

For material type 316, large test pieces, i.e. size 323 mm×123 mm, wereapplied with blends wherein the total weight of 2 gram calculated onsilicon and boron in the blend without any binder, i.e. lacquer on eachlarge test piece. The calculated amount of silicon and boron correspondsto approximately 0.05 mg/mm². The test-pieces were coated with blendA3.3, using elemental Si and elemental B in the blend. The ratios ofsilicon and boron in blend A3.3 can be found in Table 4. Each coatedtest piece were dried and cured at less than 400° C. in air. In testswith 316, except for the belt furnace test, the large test pieces wereused. For the belt furnace test the test piece were adjusted to the maxwidth of the furnace. For the other materials 2-6 different sizes oftest pieces were used, but the all applied with 0.05 mg/mm² silicon andboron.

The Test Pieces were Pre-Brazed According to the Following Pre-BrazingCycles:

VC1(T)—Vacuum cycle, where T is the maximum temperature, holding time 1h at max temp.

VC2(T)—Vacuum cycle, where T is the maximum temperature, holding time 2h at max temp.

BF(T, t)—Belt furnace cycle in Hydrogen atmosphere, where T is themaximum temperature and t is the approx. time at max temp.

The Pre-Brazing Cycles which were Carried Out were:

Nickel Type 200, Monel 400, and Hastelloy C2000 Tests,

1) VC1(1100° C.) cycle

Stainless Steel Type 316 Tests

2) VC2(1040° C.) cycle

3) VC2(1060° C.) cycle

4) VC2(1070° C.) cycle

5) VC2(1080° C.) cycle

6) VC2(1090° C.) cycle

7) VC2(1100° C.) cycle

8) VC2(1110° C.) cycle

9) VC2(1120° C.) cycle

10) VC2(1130° C.) cycle

11) VC2(1140° C.) cycle

12) VC2(1160° C.) cycle

13) VC2(1180° C.) cycle

14) VC2(1200° C.) cycle

15) BF(1100° C., 10 min) cycle

16) BF(1130° C., 10 min) cycle

Analysis of Cross-Section of the Test Pieces.

The cross-sections of all pretreated materials were analyzed usingSEM-EDX (Scanning Electron Microscope-Energy Dispersion Spectroscopy).In the cross-sections the composition for the obtained braze alloy layerwere analyzed. The silicon content as a function of the depth from theplate surface where the blend had been applied was measured. The resultsof the analysis are summarized in Table 16.

TABLE 16 Silicon Content at Different Depth from the Surface of theBraze Alloy Layer [wt %] Test No. 15 μm 30 μm 45 μm 60 μm 75 μm 90 μm105 μm 120 μm  1) Ni 200 3-4 3-4 3-4 3-4 3-4 2-3 2-3 2-3  1) Monel 4001.5-5   1.5-5   1.5-5   1.5-5   1.5-5   <0.3 <0.3 <0.3  1) C2000 3-6 3-63-6 <0.1 <0.1 <0.1 <0.1 <0.1  2) 316 5-6 5-6 5-6 5-6 <0.6 <0.6 <0.6 <0.6 3) 316 5-6 5-6 5-6 5-6 <0.6 <0.6 <0.6 <0.6  4) 316 6-7 6-7 6-7 6-7 6-7<0.6 <0.6 <0.6  5) 316 5-7 5-7 5-7 5-7 5-7 <0.6 <0.6 <0.6  6) 316 5-65-6 5-6 5-6 5-6 <0.6 <0.6 <0.6  7) 316 4-6 4-6 4-6 4-6 4-6 <0.6 <0.6<0.6  8) 316 5-7 5-7 5-7 5-7 5-7 <0.6 <0.6 <0.6  9) 316 4-7 4-7 4-7 4-74-7 4-7 4-7 <0.6 10) 316 4-8 4-8 4-8 4-8 4-8 <0.6 <0.6 <0.6 11) 316 3-83-8 3-8 3-8 3-8 <0.6 <0.6 <0.6 12) 316 4-7 4-7 4-7 4-7 4-7 <0.6 <0.6<0.6 13) 316 3-7 3-7 3-7 3-7 3-7 <0.6 <0.6 <0.6 14) 316 3-6 3-6 3-6 3-63-6 <0.6 <0.6 <0.6 15) 316 4-9 4-9 4-9 4-9 <0.6 <0.6 <0.6 <0.6

The results from the tests show that there are formed layers on top ofthe parent materials. The silicon contents are approximate ranges, butdiffer substantially from the content of silicon in the parent material,i.e. less than 0.6 wt %. The tests results show that the temperature hasan effect on the formed braze alloy layer, but the results are moredependent on the type of parent material.

Magnetic Analysis and Analysis of Shape for the Pretreated 316 Materials

Two of the pretreated materials were analyzed, nr 7, VC(1100° C.) and nr15 BF(1100° C., 10 min). Both pretreated samples showed magneticproperties for the surface layer, clearly different from the parentmaterial, the non-magnetic stainless steel type 316. The magneticproperties were confirmed since it was possible to lift the pre treatedsamples but not the “non treated samples” with a permanent magnet. Alsothe shape was changed for the pretreated samples. When inspecting thepre treated plates ocular it was confirmed that the plates were bentwith the pre treated surface facing outwards for the created convexsurface. This also means that if the material does not have thepossibility to deform a (as for this case, a thin plate), or if thematerial is pre treated on both sides, pressure stresses will be presentin the surface. Pressure stresses can e.g. increase the pressure fatigueproperties.

Surface Hardness Tests:

The obtained braze alloy surface layers were tested for hardness. Thesamples which were tested were Nickel type 200, Monel 400, HastelloyC2000, Stainless Steel Type 316 from test sample 15 BF(1100° C., 10 min)and Stainless Steel Type 316 from test sample 16 BF(1130° C., 10 min)applied both with A3.3 made with Si and B and A3.3 made with Si and B₄C.The results are summarized in Table 17.

TABLE 17 Depth from braze alloy surface HV 0.05 [μm] Monel 400, VC1(1100° C.), applied with A3.3 660 29 660 47 310 62 278 105 258 203 224217 210 262 Nickel 200, VC1 (1100° C.), applied with A3.3 401 14 396 29258 47 221 83 234 126 Hastelloy 2000, VC1 (1100° C.), applied with A3.3441 15 404 25 288 50 267 77 255 92 241 119 244 161 SS Type 316 BF (1100°C., 10 min), applied with A3.3 374 26 298 33 330 44 277 77 274 108 SSType 316 BF (1130° C., 10 min), applied with A3.3 with elemental B 78714 277 29 228 48 201 96 178 151 231 218 SS Type 316 BF (1130° C., 10min), applied with A3.3 with B₄C 909 17 589 48 261 53 253 77 227 134 213168 SS Type 316 VC2 (1100° C.), applied with A3.3 1049  22 509 32 326 52265 69 229 105 207 168 SS Type 316 VC2 (1200° C.) applied with A3.3 53218 261 38 243 61 224 80 222 128 229 169Results:

The hardness tests show that the hardness of the braze alloy layer isharder than the parent materials. All tested parent materials hadhardness less than approx. 300 HV0.05 after a heat pre-treatment cycleor a braze cycle. The hardness of the surface layer and the parentmaterial was measured from the parent material original surface to adepth of app 200 um. The increased hardness values was correlated to theearlier measured increase in Si in the surface layer, the braze alloy.The tests show also that the hardness is higher at the surface thanclosed to the parent materials.

Example 12: Brazability Tests

In this Example the obtained braze alloy layers from Example 11 weretested, such as samples number 2 to 14. One extra sample was tested andit was sample number 17, wherein the material was untreated SS type 316with applied blend. The tests were carried out for the purpose offinding out if a braze joint could be created between a substrate havinga braze alloy layer and another substrate without any braze alloy layer.

The test pieces were plates SS type 316, and the brazing tests werecarried out in normal brazing cycles. The test was performed by placingthe pre-treated test-plate with the braze alloy layer facing up. Acircular pressed plate without any braze alloy, see FIG. 1, was placedon top of the pre-treated test-plate on the braze alloy layer. A weightwas applied on the circular pressed plate to hold it in contact with thepre-treated test-plate. The test-plate sample was then exposed to aVC1(T)-cycle in vacuum at a temperature of 1210° C. The result ispresented as the size of the brazing area as a function of thepre-treatment temperature. The samples were cut across the circularpressed plate and the width of the center of the obtained joint wasmeasured according to FIG. 2. In Table 18 the average center width ofeach test samples are summarized.

TABLE 18 Pre-treatment temp Center Width Sample No. [° C.] [mm] 1 10002.56 2 1040 2.45 3 1060 2.53 4 1070 2.53 5 1080 2.18 6 1090 2.14 7 11002.25 8 1110 1.99 9 1120 1.91 10 1130 2.25 11 1140 1.21 12 1160 1.87 131180 0.78 14 1200 0.00

The results of these tests show that the higher pre-brazing temperaturethe less brazed joint, i.e. the braze alloy layer of the pre-brazedsamples loses the property to braze joints. Small center width is aresult of low brazing property. By losing the brazing property thepre-brazed samples cannot be used for brazing without adding a brazingalloy or adding additional blend of boron and silicon after thepre-brazing step. The critical temperature depends on the parentmaterial. If the parent material has a high melting point then theobtained braze alloy layer could still have brazing property at a higherpre-brazing temperature.

Example 13: Tensile Tests

Six different parent materials were tested in Example 13. The testsamples were applied with different bends, the blends were A3.3, B2 andC1, all made using Si and B as melting point depressant sources, in alacquer from Akzo Nobel (if nothing else stated). Large test pieces ofparent materials, i.e. size 323 mm×123 mm, were applied with blends. Thetotal weight of 2 g calculated on silicon and boron in the blend withoutany binder, i.e. lacquer on each large test piece, were applied on thelarge test pieces. The calculated amount of silicon and boroncorresponds to approximately 0.05 mg/mm².

The samples were of following parent materials:

1. SS Type 316 thickness 0.4 mm

2. Ni Type 200 thickness 0.45 mm

3. Monel 400 thickness 1.0 mm

4. SS Type 254SMO thickness 0.4 mm

5. Mild Steel thickness 0.4 mm having an iron content >97 wt %

6. Hastelloy C2000 thickness 0.5 mm

In this example samples of braze alloy layered materials were testedaccording to Example 11, sample 1 (Hastelloy C2000).

In these tests two pieces were cut for each tensile test sample. One ofthe test pieces was cut from a non-treated plate of the same parentmaterial as for the pre-treated piece, i.e. the braze alloy layeredpiece, see Example 11, or with a surface applied with blend A3.3dispersed in a lacquer from Akzo Nobel. The size of the test pieceswere, length 41-45 mm, and width 11.3-11.7 mm. Each test piece was bentin the middle, using a pressing tool. The shape of the upper part of thepressing tool was a 3 mm thick plate approx. 150 mm long. The lower partof the tool is made of a thick plate with a “machined groove” with aradius of 1.9 mm. When pressing, the test piece were applied on thelower pressing tool with the pre-treated surface facing downwards, whereafter the plates were pressed/bent in the middle of the length whenpressed. Sometimes an extra bending was made by hand after the pressing,e.g. if the material had a large spring back or were “too thick”.

Fixturing of the Samples

A first bent test piece with the pre-treated surface or applied surfacewas placed with the treated surface facing upwards when placed onto a 1mm plate (22×22 mm) with “non-wetting” properties. This plate togetherwith the first bent test piece was then mounted into the diagonal of atube having a square cross section. The dimensions of the tube were17×17 mm inside and 20×20 mm outside. The thickness of the tube was app1.4 mm and the height 55 mm.

A second bent non-treated test piece was placed that the curved part ofthe second test piece was placed on top of the curved part of the firstbent test piece. The second test piece was placed in the tube inperpendicular direction to the first test piece creating a small contactarea between the two pieces. The fixtured samples were then heated in aVC1(1210° C.) cycle.

Tensile Tests

The brazed tests samples were after brazing mounted in a tensile testmachine “Instron Corporation Series IX Automated Materials TestingSystem”. The Crosshead Speed was approx. 1 mm/min. The load was measuredin kN. Tensile test results, both for pre-treated (PRE) samples and notpre-treated samples are summarized in Table 19.

TABLE 19 Average load at max load Sample [kN] Hastelloy C 2000 BrazeAlloy Layered product 1.144 A3.3 Lacquer 1.330 B2 Lacquer 1.214 C1Lacquer 1.325 Ni Type 200 Braze Alloy Layered product 0.359 A3.3 Lacquer0.360 Monel 400 (1140° C.) Braze Alloy Layered product 1.522 A3.3Lacquer 1.487 SS Type 254SMO Braze Alloy Layered product 1.525 A3.3Lacquer 1.298 C1 Lacquer 0.802 SS Type 316 Braze Alloy Layered product1.166 BF(T, t)-cycle (carried out in hydrogen (atm) at a temperature of1100° C.) A3.3 Lacquer 1.693 B2 Lacquer 1.602 C1 Lacquer 1.565

Table 19 shows that brazed joints from samples with braze alloy layerhave comparable tensile strength as brazed joints from samples, whichhave a blend of silicon and boron dispersed in a binder applied on thesurface. These tests results show therefore that the selection ofbrazing method may depend on other aspects than expected tensilestrength of the produced joints.

The invention claimed is:
 1. A method for providing a braze alloylayered product comprising the following steps: applying a mechanicalblend on at least a part of a surface of a substrate, wherein themechanical blend is a mechanical blend of at least one powder ofparticles of a silicon source, in which each particle is of a siliconsource, and at least one powder of particles of a boron source, in whicheach particle is of a boron source, wherein the particles have anaverage particle size less than 250 μm wherein the at least one boronsource and the at least one silicon source are oxygen free except forinevitable amounts of contaminating oxygen, wherein the amount ofinevitable amount of oxygen is less than 10 wt %, and wherein the weightratio in the blend of boron and silicon is within a range from about3:100 to about 100:3, and wherein silicon and boron are present togetherin the blend in at least 35 wt %, and wherein the substrate comprises aparent material having a solidus temperature above 1100° C.; heating thesubstrate having the applied boron source and the applied silicon sourceto a temperature lower than the solidus temperature of the parentmaterial of the substrate to form a braze alloy; and cooling thesubstrate having the applied boron source and the applied siliconsource, and obtaining a layer of braze alloy on the substrate, whereinthe layer of braze alloy comprises the silicon source, the boron sourceand the elements of the parent material, wherein the braze alloy layerhas a melting point lower than the parent material; wherein the siliconsource is one or more of elemental silicon, an alloy containing silicon,or a compound containing silicon; and wherein the boron source is one ormore of elemental boron, an alloy containing boron, or a compoundcontaining boron.
 2. The method according to claim 1, wherein the atleast one boron source and the at least one silicon source is the samesource.
 3. The method according to claim 1, wherein the boron source isselected from elemental boron, boron carbides, nickel borides, orsilicon borides.
 4. The method according to claim 1, wherein the siliconsource is selected from elemental silicon, ferro silicon, ironsilicides, silicon carbides, or silicon borides.
 5. The method accordingto claim 1, wherein the method comprises applying a compositioncomprising the blend and at least one binder, wherein the at least onebinder is selected from solvents, water, oils, gels, lacquers, varnish,binders based on monomers, polymers, waxes, or combinations thereof. 6.The method according to claim 1, wherein the method comprises applying acomposition comprising the blend and at least one binder, wherein the atleast one binder is selected from polyesters, polyethylenes,polypropylenes, acrylic polymers, met acrylic polymers, polyvinylalcohols, polyvinyl acetates, polystyrenes or waxes or combinationsthereof.
 7. The method according to claim 1, wherein the applying stepcomprises applying a composition comprising the blend, at least onebinder, and particles of a parent material, and wherein the parentmaterial is present in an amount less than 75 wt % calculated on thetotal weight of silicon, boron and parent material.
 8. The methodaccording to claim 1, wherein the applying step comprises applying acomposition comprising the blend, at least one binder, and particles ofa braze alloy.
 9. The method according to claim 1, wherein the parentmaterial is selected from iron based alloys, nickel based alloys,chromium based alloys, copper based alloys, or cobalt based alloys. 10.The method according to claim 1, wherein said parent material comprisesfrom about 15 to about 22 wt % chromium, from about 8 to about 22 wt %nickel, from about 0 to about 3 wt % manganese, from about 0 to about1.5 wt % silicon, optionally from about 1 to about 8 wt % molybdenum,and balanced with iron.
 11. The method according to claim 1, wherein thesubstrate is a parent material and the parent material comprises morethan 50 wt % Fe, less than 13 wt % Cr, less than 1 wt % Mo, less than 1wt % Ni and less than 3 wt % Mn.
 12. The method according to claim 1,wherein the substrate is a parent material and wherein the parentmaterial comprises more than 10 wt % Cr and more than 60 wt % Ni. 13.The method according to claim 1, wherein the substrate is a parentmaterial and wherein the parent material comprises more than 15 wt % Cr,more than 10 wt % Mo, and more than 50 wt % Ni.
 14. The method accordingto claim 1, wherein the substrate is a parent material and wherein theparent material comprises more than 10 wt % Fe, 0.1 to 30 wt % Mo, 0.1to 30 wt % Ni, and more than 50 wt % Co.
 15. The method according toclaim 1, wherein the substrate is a parent material and wherein theparent material comprises more than 80 wt % Ni.
 16. The method accordingto claim 1, wherein the method comprises heating the substrate having asurface layer of the applied blend to a temperature higher than themelting point of the braze alloy.
 17. The method according to claim 1,wherein the method comprises heating the substrate having a surfacelayer of the applied blend to a temperature higher than 900° C.
 18. Themethod according to claim 1, wherein elements of the surface of thesubstrate and the blend are alloyed in the heating step to obtain amolten phase.
 19. The method according to claim 1, wherein the methodfurther comprises an additional step before the applying step, saidadditional step comprises cutting or forming or combinations thereof ofthe substrate.
 20. The method according to claim 1, wherein the methodfurther comprises an additional step before the applying step or afterthe applying step or after the heating step, said additional stepcomprises cutting or forming or combinations thereof of the substrate.